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Role of Microbes in Fermented Food
#1
Fermentation is the process of controlling microbes (bacteria, yeast, and moulds) to modify food, producing a desired product.

Often we talk about the negative issues caused by microorganisms in food such as food spoilage. But they can be used as efficient live factories to produce health beneficial food. Without some microorganisms, production of certain food items may not be possible or may be costly. Microbes are cheap resources that consist of numerous enzymes which can convert complex chemical structures into simple digestible molecules with a high efficiency. These microorganisms use the nutrients in the food as the substrate to produce energy and other required precursors for their growth in which a fermented food results. There are numerous examples for fermented food.

Fish sauce
In production of fish sauce, uneviscerated fish is mixed with salt and placed in fermented tanks to allow liquefaction for about six months. The collected liquid is further ripened for few more months. Halophillic microbes are involved in this fermentation process. Streptococcus, Micrococcus and Bacillus species predominate. This product is dark coloured with a distinct aroma.

Sauerkraut
This refers to fermented cabbage. Normal microflora in cabbage is involved in the fermentation process under anaerobic conditions. Leuconostoc mesenteroides and Lactobacillus plantarum is involved. Temperature is a crucial factor in the control of fermentation. If the temperature is below 21 degrees Celcius, Lactobacilli outgrow. L. mesenteroides require a lower temperature below 21 0C. Acidity created by Lactobacilli prevent the growth of L. mesenteroides.
Pickels
Pickels consist of vegetables like cucumber, onions, chilies etc. Lactic acid bacteria such as Leuconostoc mesenteroides, P. cerevisiae, L. brevis, L. plantarum are involved in the fermentation process These bacteria also take part in fermentation of olives.

Soy sauce
In production of soy sauce, a mixture of soybean and wheat flour is inoculated with Aspergillus oryzae and Aspergillus soyae. These fungi digest complex starch and produce sugars which facilitate the growth of bacteria. Anaerobic bacteria carry out fermentation to produce soy sauce.

Beer and Ale
Malted beverages are produced by brewing. Mainly the yeasts are involved in the process. Yeasts convert fermentable sugars to ethanol and carbon dioxide. As yeasts do not produce enough amylases to hydrolyze starch in barley grains, they are germinated prior to brewing. Hops which are added for bitterness have an inhibitory effect on gram positive bacteria. Saccharomyces carlsbergensis is the principle organism used. This species is subjected to various genetic modifications to increase the efficiency of the fermentation. In addition to ethanol and carbon dioxide, yeasts produce a small amount of glycerol, acetic acid and aromatic esters. Ale is a top fermented beverage with Saccharomyces cerevisiae.

Wine
Wine is made from grape juice in large scale. Yests; Saccharomyces cerevisiae var. ellipsoideus is the culture used in wine fermentation. High temperature is not suitable for this fermentation as yeasts die while low temperature allows the growth of lactic acid bacteria.

Environmental factors such as acidity, pH, oxygen level, moisture level, temperature, sugar content are important for this fermentation processes. In most food commodities, acidity is developed by microorganisms. This developed acidity is important for preserving the food. Proteolytic action may bring down the pH to a higher value. Some yeasts produce alkaline by products such as ammonia in their regular metabolism which is encouraged in the production of limburger cheese.

Alcohol, which is a byproduct of many fermentation pathways also have a preservative action. Alcohol content produced will depend on the sugar content, type of yeast involved in fermentation, temperature and the oxygen level. Most yeast can’t tolerate high alcohol levels.
Temperature has a direct effect on microbial fermentation which in turn affects the final quality of the product. Sauerkraut production is an ideal example to show the importance of temperature in fermentation process.
Microorganisms have different oxygen requirements for their growth and fermentation. In wine production, yeasts grow best under aerobic conditions. In baking, anaerobic conditions favour the quality of the final product. Vinegar production involves anaerobic as well as aerobic fermentation.
#2
There are lot of species of microorganism being used in various fermentation process. Here is the list of microorganism, Type of microorganims (Either Bacteria / Fungus) and thier use in food / beverage industries respectively:-

Microorganism :-Acetobacter fabarum
Type of microorganims :- bacterium
Used in fermentation of : -chocolate

- Acetobacter fabarum
- bacterium
- coffee

- Acetobacter lovaniensis
- bacterium
- vegetables

- Acetobacter malorum
- bacterium
- vinegar

- Bacillus sphaericus
- bacterium
- stinky tofu

- Bacillus stearothermophilus
- bacterium
- chocolate

- Bacillus subtilis
- bacterium
- chocolate

- Bacillus subtilis
- bacterium
- natto

- Bifidobacterium adolescentis
- bacterium
- yogurt

- Bifidobacterium lactis
- bacterium
- dairy

- Candida colliculosa
- fungus
- cheese

- Candida colliculosa
- fungus
- kefir

- Debaryomyces kloeckeri
- fungus
- Limburger cheese

- Dekkera bruxellensis
- fungus
- beer

- Enterococcus faecalis
- bacterium
- soy sauce

- Enterococcus faecium
- bacterium
- Manchego cheese

- Enterococcus faecium
- bacterium
- ham

- Enterococcus faecium
- bacterium
- pickle

- Lactobacillus acetotolerans
- bacterium
- fruit

- Lactobacillus acetotolerans
- bacterium
- vegetables

- Lactobacillus acidifarinae
- bacterium
- sourdough bread

- Lactobacillus cacaonum
- bacterium
- chocolate

- Lactobacillus casei
- bacterium
- Idiazabal cheese

- Lactobacillus casei
- bacterium
- Manchego cheese

- Lactobacillus casei
- bacterium
- Roncal cheese

- Lactobacillus casei
- bacterium
- yogurt

- Lactobacillus johnsonii
- bacterium
- dairy

- Lactobacillus johnsonii
- bacterium
- sourdough bread

- Lactobacillus rhamnosus
- bacterium
- Grana Padano cheese

- Lactobacillus rhamnosus
- bacterium
- Parmigiano-Reggiano cheese

- Leuconostoc spp.
- bacterium
- olive

- Leuconostoc spp.
- bacterium
- wine

- Proteus vulgaris
- bacterium
- surface-ripened cheese

- Pseudomonas fluorescens
- bacterium
- yogurt

- Tetragenococcus koreensis
- bacterium
- kimchi

- Yarrowia lipolytica
- fungus
- dairy

- Zygotorulaspora florentina
- fungus
- kefir

- Zymomonas mobilis
- bacterium
- palm wine
#3
Microorganisms in food fermentation

People realized long time ago that microorganisms could improve nutritional value of the food they are eating. Some types of food that is consumed today have a hundreds or thousands year long tradition. Evidences (like excavated jars…) suggest that some fermented beverages were produced in Babylon 5000 years BC while milk fermentation started a bit “later”, around 3000 BC. Fermentation is one of the oldest methods used for food preservation. List of food that could be processed and improved by microorganisms is long as well as the list of beneficial effects fermented food has on our health.

Fermentation process increases nutritional value of the food by increasing the level of proteins, vitamins, amino-acids, essential fatty acids…It also increases food digestibility. Typical example is lactose intolerance that prevents many people from drinking milk. Microorganisms used in milk fermentation digest lactose and decrease it to the level that could be safely consumed even with lactose intolerant people. Bacterial enzymatic hydrolysis can enhance intestinal bioavailability of the fat and proteins. Disorders like constipation, irritable bowel syndrome, yeast infections and some kind of allergies could be prevented or decreased with well balanced gut microflora.

Here’s the list of some less known fermented products and their effect on the health:

Kefir is popular in Eastern European and Middle Eastern countries. This is easily digested alcoholic milk beverage that could improve immune response and is often given to immune-compromised patients like those suffering from AIDS, herpes or cancer.

Koumiss is Caucasus derived fermented dairy product used in the treatment of pulmonary tuberculosis.

Natto is fermented soybean products. This sticky meal, rich in protein, is popular in Asian kitchen and it’s believed that it prevents brain hemorrhage. Due to increased level of vitamin K2, it’s used to prevent osteoporosis in older people.

Indonesian tempeh is fermented soybean product that reduces cholesterol levels. Level of niacin and riboflavin in the tempeh could be increased with Rhizopus oligosporus starter culture.

Chinese douche is another soybean product that is effective in lowering high blood pressure.

Kimchi is Korean fermented dish that could be produced in hundreds of ways using 4 main ingredients: napa cabbage, radish, scallion, or cucumber. This meal is famous for its health benefits. It’s used to prevent constipation and colon cancer. It produces anti-stress effect, decreases cholesterol level, ameliorates depression, and prevents osteoarthritis, liver disease, obesity and atherosclerosis.

Gundruk is result of green vegetable fermentation while Sinki is fermented radish tap-root product. These Nepal derived dishes are used to prevent cancer as they contain large amounts of anti-cancerogenous substances such as lactic acids, vitamin C, carotene and fibers.

Bhaati jaanr extract is Himalayan fermented rice food-beverage that increases the strength in women after childbirth. Kodo ko jaanr is fermented finger millet product that could serve the same purpose due to high energy value.

Here are some of the most famous probiotics and their effect on the human health:

Bifidobacteria species reduce incidence of neonatal necrotizing enterocolitis.

Enterococcus faecium can decrease duration of acute diarrhea resulting from gastroenteritis.

Lactobacillus strains can ameliorate pouchitis, improve lactose digestion, decrease diarrhoea in lactose intolerant individuals or in individuals with short-bowel syndrome and improve mucosal immune function and mucin secretion.

Lactobacillus acidophilus can decrease diarrhea in patients receiving pelvic irradiation; decrease polyps, adenomas and colon cancer in experimental animals; prevent urogenital infection induced by Escherichia coli, Klebsiella pneumoniae, Pseudomonas aeruginosa; lower serum cholesterol levels.

Lactobacillus plantarum can prevent diarrhea; reduce inflammation, pain and constipation in inflammatory bowel disease; decrease bloating and flatulence; L. plantarum produces positive effect on immunity in HIV+ children.

Lactobacillus reuteri can shorten the duration of acute gastroenteritis as well as acute diarrhea.

Lactobacillus rhamnosus can enhance cellular immunity.

Lactobacillus salivarius can suppress and eradicate Helicobacter pylori in tissue cultures and animal models by lactic acid secretion.

Bacteroides species can decrease chronic colitis, gastritis and arthritis.

Saccharomyces boulardii (yeast) can reduce recurrence of Clostridium difficile diarrhea and decrease risk of antibiotic-associated diarrhea; S. boulardii can shorten duration of acute gastroenteritis and prevents functional diarrhea in irritable bowel syndrome.

Unfortunately, consumption of fermented food is repressed by modern life style and growing popularity of the fast food. It’s a shame; fermented food is not just tasty but extremely healthy and important for our well being.
#4
Apart from benefits of bacteria in food industries, some of them are causing food poisoning. For this reason, the purity of culture is important for any fermentation process. The most important part of microbial inoculums preparation is maintenance of purity which helps in avoiding unwanted microorganisms in food processing. Therefore the knowledge of bacteria which may cause or damage food is equally important. Today many bacteria has toxins and also possess the capability to cause disorders like food poisoning in humans and animals. The consumption of these foods may show symptoms like headache, fever, cold, vomiting etc.
One of such bacteria is Bacillus cereus. These bacterial groups consist of six members. These are B.anthracis, B. cereus , B. mycoides, B. pseudomycoides, B weihenstephanensis and B. thuringiensis. These species are closely related and therefore should be placed within one species. B. cereus is many times isolated from variety of foods, fruits and vegetables. This bacterium is soil inhabitant. It causes diarrhea, vomiting and illness simultaneously. It is many a times found in Desserts, meat dishes, dairy products and are associated with diarrheal illness. The toxin has been isolated from these bacteria and is characterized. It is small peptide ring synthesized by enzymes peptide synthetase.
In many outbreaks it has been observed that three typical B.cereus enterotoxins are involved. Two out of three are enterotoxins which are three component proteins and they are related. The third protein is CytK which is one component protein in nature. This species has unique characteristics to adhere to many surfaces and thus they are able to survive normal washing and disinfection.
In such scenario, one needs to have knowledge of such bacteria, their metabolism, habitat, prevention etc, so as to maintain the quality of concern products.
  

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